1. Field of the Invention
The present invention relates to voltage detection devices.
2. Description of Related Art
In hybrid electric vehicles and the like, to obtain a high voltage for driving, a battery pack is used in which a plurality of unit batteries composed of secondary battery cells are connected in series. To achieve proper charge/discharge control through monitoring of the state of the battery pack, it is necessary to correctly recognize the voltage states of the individual unit batteries. However, since a large number of unit batteries are connected in series to obtain a high voltage, the battery pack is often managed in a form divided into a plurality of blocks, with voltage detection ICs provided on a block-by-block basis. Each voltage detection IC detects the terminal voltages of the unit batteries in the corresponding block, and transmits the results of the detection to a main IC (MPU) which manages the entire battery pack. The plurality of voltage detection ICs are, with a view to reducing wiring and terminals needed, connected via a common communication line to the main IC (that is, they are connected to the main IC in a daisy-chain configuration).
To achieve exchange of signals between the main IC and the plurality of voltage detection ICs via a common communication line, unique address numbers (unique IDs) need to be assigned to the voltage detection ICs respectively.
According to one known method (hereinafter referred to as the first conventional method), an address setting terminal is added, as an external terminal, to a voltage detection IC, and by feeding a digital signal to the address setting terminal, an address number is set. For example, in a case where eight voltage detection ICs are connected to a main IC, three bits' worth of address setting terminals (that is, three address setting terminals) are added to each voltage detection IC. For another example, in a case where 16 voltage detection ICs are connected to a main IC, four bits' worth of address setting terminals (that is, four address setting terminals) are added to each voltage detection IC.
Also proposed is a second conventional method as follows (see, for example, JP-A-2009-156633). First, a main IC transmits the address number “0” to a voltage detection IC directly coupled to the main IC. Each voltage detection IC, on receiving an address number via a communication line on the main IC side, takes as its own address number an address number obtained by incrementing the received address number by one, and delivers the address number obtained by incrementing the received address number by one to a communication line on the side away from the main IC. In this way, for example, in a case where a first to a fifth voltage detection IC are connected in this order starting from the main IC, the first to fifth voltage detection ICs are assigned the address numbers “1” to “5” respectively.
With the first conventional method, terminals dedicated to address setting need to be provided on each voltage detection IC. As the number of voltage detection ICs connected increases, the number of dedicated terminals needed increases. It is however undesirable to add such dedicated terminals, because doing so restricts the package of voltage detection ICs, increases the size of voltage detection ICs, or invites other inconveniences.
With the second conventional method, each voltage detection IC needs to set an address on a voltage detection IC in the next stage (a voltage detection IC on the side away from the main IC). That is, each voltage detection IC needs to be additionally furnished with a function for address setting. Inconveniently, this complicates the entire system.